JP2002102902A - Cold rolling method of material steel sheet for hot-dip metal plating and method of manufacturing alloyed hot-dip metal-plated steel sheet - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent unevenness in the amount of coating on a galvanized steel sheet and to prevent the occurrence of alloying unevenness in a galvannealed steel sheet. SOLUTION: The surface roughness R _{Z of the} roll surface processed by shot dull processing and / or discharge dull processing is 10
Use a work roll of at least μm, or have a groove formed in the roll circumferential direction by grinding or the like. If the roll surface roughness R _Z, which is the depth of the groove, is at least 10 μm, and the groove length L ( μm) is a method for cold rolling a base steel sheet for hot-dip metal plating using a work roll satisfying the following expression (1):
A method for producing an alloyed hot-dip metal-plated steel sheet in which a hot-dip metal plating is performed on a hot-dip metal plating material steel sheet obtained by the cold rolling method, and then a hot alloying treatment is performed. L> 10 / (tan α) (μm) (1) In the formula (1), α represents a contact angle between the roll and the steel sheet for hot metal plating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cold-rolling a steel sheet for hot-dip metal plating using a tandem rolling mill and a method for producing a galvannealed steel sheet using the cold-rolling method.

[0002]

2. Description of the Related Art At the time of coil handling in a state of a hot-rolled coil before cold rolling, minute surface defects having irregularities occur on the surface of the steel sheet due to rubbing and fusion of the steel sheets. There are many cases. Minute dent defects before cold rolling, when dispensing hot picked coil to pickling equipment,
It often occurs when the steel sheet is wound up after pickling and when the coil is delivered to the cold rolling equipment.In addition, scratches due to rubbing between the steel sheets during handling in the state of the hot-rolled coil, etc. It is easy to occur not only when winding a steel sheet.

The size of the above-mentioned defects varies in size and size, but has a depth of about 10 μm. Rolling oil is confined between the rolls at the time of cold rolling at the dents of the above-mentioned defects, and remains as unrolled portions to generate oil pits. On the other hand, the present inventor peeled off the plating at the portion where the alloying unevenness occurred during the production of the galvannealed steel sheet, and measured the profile of the surface of the material steel sheet.

The obtained results are shown in FIGS. Figure 1
As shown in FIG. 3, a dent scratch having a depth of about 10 μm was found in the uneven alloying portion. Conventionally, this degree of dent was not a problem in cold rolling.However, from the above investigation results, when the cold-rolled steel sheet is a material steel sheet for hot-dip metal plating, the dent scratch It was found that the unevenness in the amount of plating applied was amplified in the portion, and when the alloying treatment was performed after plating, the unevenness in the alloying occurred in the dent scratched portion and remained as a pattern.

That is, the present inventor has reported that the presence of a dent in a cold-rolled steel sheet causes uneven coating weight in hot-dip metal plating and uneven alloying of an alloyed hot-dip coated steel sheet. It has been found that this is a major factor in reducing the yield when manufacturing a plated steel sheet.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, prevents unevenness in the amount of coating on a hot-dip coated steel sheet, and reduces the occurrence of non-uniformity in the alloyed hot-dip coated steel sheet. It is an object of the present invention to provide a method of cold rolling a material steel sheet for hot-dip metal plating which can be prevented, and a method of manufacturing an alloyed hot-dip metal-plated steel sheet using the cold rolling method.

[0007]

SUMMARY OF THE INVENTION The present inventor has found that a dent scar generated before cold rolling remains as an oil pit after cold rolling, and that the unevenness in the coating weight of the molten metal plating in the oil pit portion causes alloying. We focused on bringing about unevenness. As a result, a work roll having a groove of the same depth as the dent of the steel plate in the roll circumferential direction, more preferably having a groove-like portion of a depth and length not buried in the dent of the steel plate in the roll circumferential direction. By performing cold rolling of the material steel sheet for hot-dip metal plating using a work roll, the groove shape of the roll surface is transferred to the shoulder of the dent scratch, and oil discharge is promoted,
No oil pits were generated, and it was found that dent defects could be eliminated by rolling.

[0008] Further, after the material steel sheet for hot-dip metal plating is cold-rolled using the above-described work roll, hot-dip metal plating is performed, thereby preventing the occurrence of unevenness in the coating weight of the hot-dip metal plating. The present inventors have found that it is possible to prevent alloying unevenness in galvannealed metal plating such as galvannealed galvanizing, and have arrived at the present invention.

[0009] That is, the first aspect of the present invention is to provide a hot-rolled steel sheet for hot metal plating in cold rolling using a tandem rolling mill, wherein the surface of the roll is processed by shot dulling and / or discharge dulling. _RZ is 10
A cold rolling method for a hot-dip metal plating material steel sheet, characterized by using a work roll having a size of at least μm. The second invention has a groove formed in the roll circumferential direction when rolling a material steel plate for hot-dip metal plating in cold rolling using a tandem rolling mill, and a roll surface roughness which is a depth of the groove. R _Z
Is a work roll having a groove length of 10 μm or more and a groove length L (μm) satisfying the following formula (1).

L> 10 / (tan α) (μm) (1) A third invention is a method of rolling a material steel plate for hot-dip metal plating in cold rolling using a tandem rolling mill. The roll surface roughness R _Z, which is the depth of the groove, is 10 μm or more, and the length L (μm) of the groove is expressed by the following formula:
A cold rolling method for a raw steel sheet for hot-dip metal plating, characterized by using a work roll satisfying (2).

L> R _Z / (tan α) (μm) (2) In the above formulas (1) and (2), α is a roll and a material steel sheet for hot-dip metal plating which is a material to be rolled. Contact angle, ie,
It shows the angle between the arc portion where the steel plate and the roll are in contact and the center of the roll. In the first to third inventions described above, it is preferable that the work roll is a work roll of a stand before a final stand of a tandem rolling mill composed of a plurality of stands (suitable for the first invention). Aspects, preferred aspects of the second invention, and preferred aspects of the third invention).

The first to third inventions, the preferred embodiment of the first invention to the preferred embodiment of the third invention, more preferably, the material steel sheet for hot-dip galvanizing, which is a material steel sheet for hot-dip galvanizing. Applied as a cold rolling method. A fourth invention is a method of hot-dip coating a raw steel sheet for hot-dip metal plating obtained by the cold rolling method according to the first to third inventions, the preferred embodiment of the first invention to the preferred embodiment of the third invention. A method for producing an alloyed hot-dip metal-plated steel sheet, comprising subjecting a metal plating to a heat alloying treatment.

The above-mentioned fourth invention is more preferably
The material steel sheet for hot-dip galvanizing is applied as a method for producing an alloyed hot-dip galvanized steel sheet that is a material steel sheet for hot-dip galvanizing. The surface roughness R _Z in the first to fourth inventions indicates a two-dimensional surface roughness R _Z measured in the roll axis direction, and is a ten-point average roughness defined in JIS B 0601-1994. Indicates

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The present inventor has a work roll having a groove of the same depth as the dent scratch of the steel plate in the roll circumferential direction, more preferably,
By performing cold rolling using a work roll having a groove portion having a depth and a length in the roll circumferential direction that is not buried in the dent of the steel plate, the groove shape of the roll surface is transferred to the shoulder of the dent. It has been found that oil discharge is promoted, oil pits can be prevented from occurring, and dent defects can be eliminated.

Further, by subjecting the raw steel sheet for hot-dip metal plating to cold rolling using the above-mentioned work rolls and subjecting the obtained steel sheet to hot-dip metal plating, it is possible to prevent the occurrence of unevenness in the coating weight of the hot-dip metal plating. As a result, they have found that it is possible to prevent alloying unevenness in alloyed hot-dip metal plating. Hereinafter, the present invention will be described in the order of I. cold rolling method, and II.

[I. Cold Rolling Method:] As the material steel sheet for hot-dip metal plating in the present invention, a steel sheet made of ordinary steel having a carbon content of 0.02% by mass or less (hereinafter, mass% is referred to as%) is used. It is preferable to use According to a first aspect of the present invention, when cold rolling a raw steel sheet for hot-dip metal plating, a surface roughness R _{Z obtained} by processing a roll surface by shot dulling and / or electric discharge dulling, preferably at a front stand of a tandem rolling mill. Is a cold rolling method using a work roll of 10 μm or more.

According to the first aspect of the present invention, the random irregularities formed on the roll surface are transferred to the shoulders of the dents and scratches on the steel sheet to promote the discharge of oil, thereby preventing the generation of oil pits. Rolling can eliminate dent defects. As a result, the material steel sheet for hot-dip metal plating is cold-rolled using the above-described work roll, and the resulting steel sheet is subjected to hot-dip metal plating. It is possible to prevent alloying unevenness in the galvannealed metal plating.

In the first aspect, the roll preferably has a surface roughness R _Z of 50 μm or less. This is because, when the surface roughness R _Z of the roll exceeds 50 μm, the dent defect erasing effect is saturated in practical use, the roll processing requires man-hours, and the friction coefficient at the time of rolling becomes too high. Because it becomes difficult.

In the first aspect of the present invention, it is preferable that the work roll described above is disposed on a stand before the final stand of the tandem rolling mill. this is,
By arranging the above work roll as a work roll of the stand before the last stand, the dent defect is eliminated by the former stand, and even if the oil cannot be completely discharged by the former stand, the discharge groove is already formed. Therefore, the oil is discharged at the subsequent stand, and the dent defect disappears by rolling.

That is, for example, in the case of a five-stand cold rolling tandem mill, the first stand and / or the second stand
The stand uses a work roll subjected to shot dull processing or electric discharge dull processing, and the other stand uses a grinding roll generally used in cold rolling. In addition,
The work roll of the final stand (the fifth stand in the case of five stands) uses a roll having a surface roughness corresponding to a target plate surface roughness. Can be selected.

The second invention is a more preferred cold rolling method in the present invention, wherein when rolling a raw steel sheet for hot-dip metal plating, preferably by grinding the roll surface in a former stage of a tandem rolling mill. It has a groove formed in the roll circumferential direction, the roll surface roughness R _Z which is the depth of the groove is 10 μm or more, and the groove length L (μm) is expressed by the following formula.
This is a cold rolling method using a work roll satisfying (1).

L> 10 / (tan α) (μm) (1) In the above formula (1), α is the contact angle between the roll and the steel sheet for plating, which is the material to be rolled, that is, the steel sheet and the roll Indicates the angle formed between the contacting arc portion and the center of the roll. The length L of the groove on the roll surface can be measured by microscopic observation using a replica of the roll surface.

Α can be actually measured from the relationship between the length of the roll bite portion of the material to be rolled and the roll diameter. That is, α can be determined from the relationship between the length of the roll bite portion (contact arc length) and the roll diameter by actually measuring the surface shape of the steel plate that has been in contact with the roll after the rolling is stopped.

Further, as shown in FIG. 4, tan α can be approximately obtained from the roll radius and the amount of reduction. In addition, in FIG. 4, 1 is a work roll, 2 is a rolling end part of the hot-dip metal plating material steel plate, and 3 is a rolling reduction of the hot-dip metal plating material steel plate. In the above-mentioned second invention, as shown in FIGS.
m Since the dent scratches before and after cause uneven coating weight of hot-dip metal plating and uneven alloying in alloyed hot-dip metal plating, the roll surface roughness R _Z (10-point average Is greater than 10 μm and the groove length L
Cold rolling is performed using a work roll whose (μm) satisfies the expression (1).

The above work roll can be obtained by shot dulling and / or discharge dulling. According to the second aspect of the present invention, a roll having a groove depth for a dent defect having a depth d of about 10 μm, which causes unevenness in coating weight of hot metal plating and uneven alloying in alloyed hot metal plating, is provided. By using a work roll having a surface roughness R _Z of 10 μm or more and a groove length L (μm) satisfying the above expression (1), the shape of the groove on the roll surface at the shoulder of the steel plate dent scratch is reduced. The transfer is performed, and the discharge of oil is further promoted, the generation of oil pits can be prevented, and the dent defect can be eliminated (FIG. 5).

As a result, the material steel sheet for hot-dip metal plating is cold-rolled using the above-mentioned work roll, and the resulting steel sheet is subjected to hot-dip metal plating, thereby preventing the occurrence of unevenness in the coating weight of the hot-dip metal plating. Thus, it is possible to prevent alloying unevenness in the galvannealing. If the groove length L does not satisfy the above expression (1), no oil discharge groove is formed at the shoulder of the dent, and the oil is not completely discharged, and an oil pit is formed.

In the second aspect of the present invention, it is preferable that the roll has a surface roughness R _Z of 50 μm or less and a groove length L of 10 mm or less. This is because when the roll surface roughness R _Z exceeds 50 μm, the groove length L is 10 mm.
In any case, the effect of eliminating the dent defect is saturated in practical use, and the roll processing requires man-hours.

In the second aspect of the present invention, it is preferable that the work roll is arranged on a stand before the final stand of the tandem rolling mill. this is,
By arranging the above work roll as a work roll of the stand before the last stand, the dent defect is eliminated by the former stand, and even if the oil cannot be completely discharged by the former stand, the discharge groove is already formed. Therefore, the oil is discharged at the subsequent stand, and the dent defect disappears by rolling.

That is, in the case of a five-stand cold rolling tandem mill, for example, the first stand and / or the second stand
The stand, using a work roll satisfying the formula (1), the other stand R _Z commonly used in cold rolling using the grinding rolls of about 2 to 5 [mu] m. In addition,
The work roll of the final stand (the fifth stand in the case of five stands) uses a roll having a surface roughness corresponding to a target plate surface roughness. Can be selected.

FIG. 6 shows that R under the condition satisfying the above expression (1).
_This shows the oil pit remaining rate when _Z is changed. In addition,
The oil pit residual ratio was determined from the number of dent scratches per unit area of each of the unrolled portion and the portion which had been rolled to the second stand for the material to be rolled which had been bittened during rolling.

As shown in FIG. 6, it can be understood that the residual ratio of oil pits can be significantly reduced by using a work roll satisfying the above-mentioned formula (1) by setting R _Z to 10 μm or more. As described above, the cold rolling method of the present invention has been described.In the present invention, in order to more reliably transfer the shape of the groove-shaped portion of the roll surface to the shoulder of the steel plate dent scratch, and to eliminate the dent defect by rolling. A work roll having grooves formed in the circumferential direction of the roll, having a groove surface depth _Rz of 10 μm or more and a groove length L (μm) satisfying the following expression (2). It is more preferable to use (third invention).

L> R _Z / (tan α) (μm) (2) [II. Alloying hot-dip metal plating:] In the present invention, the invention is obtained by the first to third inventions described above. After hot-dip metal plating is applied to the material steel sheet for hot-dip metal plating, a heat alloying treatment is performed to produce an alloyed hot-dip metal plated steel sheet.

Hereinafter, the galvannealed galvanizing, which is a typical galvannealed metal plating, will be described. In the present invention, the cold-rolled steel sheet obtained by the above-described rolling method,
Preferably, after the pickling treatment, for example, in a heating furnace disposed in a continuous hot-dip galvanizing line, the hot-dip galvanizing is performed after reducing under a reducing atmosphere.

As the hot-dip galvanizing bath, a plating bath containing 0.08 to 0.2% of Al is suitable, and the bath temperature is suitably 450 to 500 ° C. Next, after applying a coating weight control by a gas wiping method to the hot-dip galvanized steel sheet pulled up from the hot-dip galvanizing bath, it is preferably performed in an alloying furnace under the conditions of a maximum attained sheet temperature: 460 to 530 ° C. Heat alloying.

The amount of Fe diffusion into the plating layer during the alloying treatment is preferably 8 to 11% as the Fe content in the obtained plating layer.

[0036]

EXAMPLES The present invention will be described below more specifically based on examples. (Example 1) A hot-rolled steel sheet was cold-rolled using a five-stand cold-rolling tandem mill. As the steel sheet, a steel sheet made of ordinary steel having a carbon content of 0.005% was used.

The work roll of the first stand is
Surface roughness R _ZHas a 14μm groove
Using the formed work roll, the second stand to the fifth
The work roll of_Z2.5 μm work
A roll (grinding roll) was used. Cold rolled steel obtained
The oil pit remaining rate of the plate is as low as 3%, and before cold rolling
It was found that the formed dent scratch had disappeared.

Next, the obtained cold-rolled steel sheet was passed through a continuous hot-dip galvanizing line, and was subjected to pickling, heat reduction annealing, hot-dip galvanizing, and alloying. Hot-dip galvanizing and alloying were performed under the following conditions. [Hot-dip galvanizing:] Bath temperature: 465 ° C Al concentration in the bath: 0.13% [Alloying treatment:] Maximum attained plate temperature: 490 ° C The coating weight of hot-dip galvanizing is 40 g / m ^{2 on} both sides.
And

The alloyed hot-dip galvanized steel sheet was visually inspected for any non-uniform alloying, and the defect rate due to the non-uniform alloying was examined based on the weight ratio of the spots where the spot pattern was generated. Was as low as 0.4%, which reduced defective products. (Example 2) An alloyed hot-dip galvanized steel sheet was manufactured in the same manner as in Example 1 except that a work roll having a groove having a surface roughness R _Z of 13 µm formed by discharge dulling was used as the work roll of the first stand. Was manufactured.

Next, as a result of examining the defective product occurrence rate due to uneven alloying in the same manner as in Example 1, the defective product occurrence rate was found to be
As low as 0.5%, defective products could be reduced. (Example 3) A hot-rolled steel sheet was cold-rolled using a five-stand cold-rolling tandem mill. As the steel sheet, a steel sheet made of ordinary steel having a carbon content of 0.005% was used.

[0041] As the work roll of the first stand, using the work rolls of the following specification and forming the groove in the roll peripheral direction by grinding, the work roll of the second stand to fifth stand, R _Z is a 2μm work roll (Grinding roll) was used. [Specifications of the work roll of the first stand:] Roll diameter: 600 mm Surface roughness in the roll axis direction R _Z : 13 μm Groove length (L): 550 μm Contact angle (α) between the roll and the material steel plate for plating: 1.7 ° L> 10 / (tan α) = 337 μm The length L of the groove on the roll surface was measured by microscopic observation using a replica of the roll surface, and α was in contact with the roll after rolling was stopped. The cross-sectional shape of the steel sheet was measured, and determined from the relationship between the length of the roll bite (contact arc length) and the roll diameter.

The residual ratio of oil pits in the obtained cold-rolled steel sheet was extremely low at 1%. Next, the obtained cold-rolled steel sheet was passed through a continuous galvanizing line, pickled,
Heat reduction annealing, hot-dip galvanizing, and alloying treatment were performed.
Hot-dip galvanizing and alloying were performed under the following conditions. [Galvanizing:] Bath temperature: 465 ° C. bath Al concentration: 0.13% [alloying:] peak metal temperature: 490 ° C. In addition, the coating weight of galvanizing, both sides 40 g / m ²
And

Next, as a result of examining the defect occurrence rate due to uneven alloying in the same manner as in Example 1, the defect rate was found to be 0.2%.
%, And the number of defective products could be reduced. (Comparative Example) An alloyed hot-dip galvanized steel sheet was manufactured in the same manner as in Example 1 except that a work roll having the following specifications as a grinding roll was used as the work roll of the first stand.

[Specification of the work roll of the first stand:] Roll diameter: 600 mm Surface roughness in the roll axial direction R _Z : 8 μm Groove length (L): 50 μm Contact angle (α) between the roll and the steel sheet for plating _{: 1.7 ° L <R Z /} (tanα) = 270μm Next, the results of the examination of defective occurrence rate by uneven alloying in the same manner as in example 1, defective generation rate was 1.2%.

[0045]

According to the present invention, by making dent defects generated before cold rolling defect-free in cold rolling, it is possible to prevent the occurrence of uneven coating weight on a hot-dip coated steel sheet. It has become possible to prevent the occurrence of uneven alloying in alloyed hot-dip galvanizing such as alloyed hot-dip galvanizing, and to improve the yield of alloyed hot-dip galvanized steel sheets.

[Brief description of the drawings]

FIG. 1 is a graph showing a profile of a material steel plate surface in an uneven alloying portion.

FIG. 2 is a graph showing a profile of a surface of a material steel plate in an uneven alloying portion.

FIG. 3 is a graph showing a profile of a surface of a material steel plate in an uneven alloying portion.

FIG. 4 is an explanatory diagram showing a contact angle between a work roll and a material to be rolled.

FIG. 5 is a cross-sectional view (schematic view) showing a groove portion of the work roll and a steel plate dent wound portion.

FIG. 6 is a graph showing a relationship between a work roll surface roughness R _Z and an oil pit remaining rate of a cold-rolled steel sheet.

[Explanation of symbols]

 Reference Signs List 1 work roll 2 end of rolling of material steel plate for hot-dip metal plating 3 depression of material steel plate for hot-dip metal plating 4 groove of work roll 5 dent of steel plate

Claims (5)

[Claims] 1. When rolling a material steel plate for hot-dip metal plating in cold rolling using a tandem rolling mill, the surface roughness R _{Z obtained} by processing the roll surface by shot dulling and / or discharge dulling is 10 μm or more. A cold rolling method for a raw steel sheet for hot-dip metal plating, comprising using a work roll described above. 2. When rolling a steel sheet for hot-dip metal plating in cold rolling using a tandem rolling mill, the roll has a groove formed in the circumferential direction of the roll, and a roll surface roughness R which is a depth of the groove. _{When Z} is 10 μm or more, the groove length L (μm) is calculated by the following formula.
A cold rolling method for a raw steel sheet for hot-dip metal plating, characterized by using a work roll satisfying (1). L> 10 / (tan α) (μm) (1) In the above formula (1), α represents the contact angle between the roll and the material steel plate for hot-dip metal plating as the material to be rolled. 3. When rolling a raw steel sheet for hot-dip metal plating in cold rolling using a tandem rolling mill, the roll has a groove formed in the circumferential direction of the roll, and a roll surface roughness R which is a depth of the groove. _{When Z} is 10 μm or more, the groove length L (μm) is calculated by the following formula.
A method for cold rolling a steel sheet for hot-dip metal plating, comprising using a work roll satisfying (2). L> R _Z / (tan α) (μm) (2) In the above formula (2), α represents a contact angle between the roll and the material steel sheet for hot-dip metal plating as a material to be rolled. 4. The cold rolling of a material steel sheet for hot-dip metal plating according to claim 1, wherein the work roll is a work roll of a stand before a final stand of a tandem rolling mill. Method. 5. An alloy characterized by subjecting a material steel sheet for hot metal plating obtained by the cold rolling method according to claim 1 to hot metal alloying after subjecting the steel sheet to hot metal plating. Production method of heat-hardened metal-plated steel sheet.